Rhenium (Re) is a particularly rare metal among rare metals, and is used to reinforce turbine materials for aircrafts, for example.
As a conventional process for producing metallic Re, a process is known in which ammonium perrhenate rhenium (NH4ReO4; (APR)) as an intermediate product is obtained from an ore, and reduced in a hydrogen stream at approximately 150° C. to obtain metallic Re.
Moreover, generally, rare earth metals, e.g., neodymium (Nd) and dysprosium (Dy) used as a raw material for magnets are difficult to separate individually because these elements have similar chemical properties.
As a conventional process for isolating these metallic Nd and Dy, a process is known in which an ore is dissolved with sulfuric acid and the like; subsequently, impurities such as alkali metals and platinum group metals are separated and removed by an oxalic acid precipitation method; and rare earth metals are separated from each other and reduced with calcium fluoride.
As an alternative process for isolating these rare earth metals, a process is known in which rare earth metals are separated from each other and recovered by volatilizing oxides of the rare earth metals in a molten salt (for example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-201765)).
Unfortunately, in the conventional processes, consumption of acids, alkalis, organic solvents, and ion exchange resins produces a large amount of secondary wastes in the course that APR as an intermediate product in production of metallic Re is produced.
As another problem, the oxides of the rare earth metals such as Nd and Dy have a slow reduction rate, and it is difficult to reproduce a reducing agent used, again leading to production of a large amount of secondary wastes.
On the other hand, there has been no report on a technique to independently separate metallic Re and rare earth metals such as metallic Nd and metallic Dy and recover those metals through a series of steps.